Apparatus for limiting the degree of subatmospheric pressures



March 4, 1952 o. H. P. DAWSON 2,588,214

APPARATUS FOR LIMITING THE DEGREE OF SUBATMOSPHERIC PRESSURES Filed Jan. 2, 1947 Mercury Reservoir A Small Tube Fritted Gloss Pluie 0M 11 00W INVENTOR.

Patented Mar. 4, 1952 APPARATUS FOR LIMITING THE DEGREE O1: SUBATMQ SPHERIG, PRESSURES Oliver H. P. Dawson, Baytown, Tex., assignor, by mesne assignments, to Standard Oil Development Company, Elizabeth, N. .L, a corporation of Delaware Application January 2, 1947, Serial No. 719,885

4'Cla1imSa (Cl. 137--78) The present invention is directed to an apparatus for controlling pressures. More particularly, the invention is directed to a device for automatic control of subatmospheric pressures.

In the distillation of petroleum, particularly in the distillation of lubricating oil fractions from petroleum, it is necessary to distill the oils at reduced pressures; otherwise, the temperature at which the oil would have to be subjected to distill at atmospheric or elevated pressures might cause thermal decomposition of the lubricating oil fractions with accompanying impairment of the quality of the product. Accordingly, it is desirable to distill lubricating oils at pressures substantially below atmospheric pressures.

In the handling and distilling of many organic compounds, it is also necessary to employ reduced pressures. Various drying operations, for example, require the application of subatmospheric pressures. Quite often in the control of these distillin and evaporating techniques, it is desirable to control the pressures within very narrow ranges. If the pressures are not controlled, considerable deterioration in quality of the organic compound by evaporation, distillation, and other handling might result.

It is, therefore, the main object of the present invention to provide a device which automatically controls pressures.

Briefly, the present invention may be described a as a manometric apparatus including a reservoir for a heavy metal such as mercury, a capillary tube which serves as an arm of the manometer, and an inclined arm connecting the capillary tube and the mercury reservoir through a flexible connection, a flexible connection connecting another arm of the manometer to an exhaustion means, the capillary tube manometer and the side arm being separated by a plate pervious to gases and impervious to a liquid heavy metal.

The apparatus of the present invention will be further illustrated by reference to the drawing in which the single figure is an elevational view of one embodiment thereof.

Referring now to the drawing, numeral ll designates a reservoir for a fluid heavy metal, such as mercury. The lower end of reservoir II terminates into a pipe l2 which is flexibly connected by means offlexible tube l3 with an inclined tube M to which are attached manometer arm I 5 and a second arm l6. Manometer arm [5 and second arm it are separated by a gas pervious and a fluid heavy metal impervious plate IT.

The arms l5 and I6 may be suitably raised or is open to the atmosphere.

lowered as the case may be by manipulation ofclamp I8 which is slidably arranged on vertical rod I9 aifixed to plate 20.

The manometer arm I5 is a small tube which The arm I6 is substantially larger in diameter than manometer arm [5 and is connected by means of a flexible tube 2| to a side arm 22 sealed into the pipe 23 forming the outlet from reservoir ll. Pipe 23 has a second side arm 24 which communicates with the pressure source which is to be controlledwhile the outlet 23 is in fluid communication with an exhaustion means. I

The side arm 22 is provided with an auxiliary valve 25 which will be described further hereinafter.

It will be seen from the foregoing description that the gas pervious plate is joined by means of a T to the lower side of a mercury manometer which comprises manometer arm l5, mercury reservoir ll, pipe [2, flexible tube I3, and inclined arm l4. In the operation of the device of the present invention, the side arm 24 is connected to the source of pressure to be controlled through side arm 24 while the outlet 23 is connected to an exhaustion means such as a vacuum pump. The height of the mercury in reservoir I l is set at some arbitrarily chosen point such as 740 mm. as indicated by the dotted lines 26. As the pressure fluctuates, the plate pervious to air but impervious to fluid heavy metal is alternately covered and uncovered. When the gas-pervious plate is uncovered, air is admitted through the pervious plate and into the exhaustion means thus adjusting the reduced pressures, allowing the liquid heavy metal to return to cover the plate and interrupt the flow of air. By alternately covering and uncovering the plate, a substantially constant pressure may be maintained on the system. To add sensitivity to the device, the manometer may be inclined at the point where the gas-pervious plate is located and the high side of the manometer, that is the reservoir ll, may be enlarged so that the slightest change in pressure will be multiplied many times.

It will often be found desirable to employ the device of the present invention in the following manner. The mercury reservoir II is initially approximately one-half full of mercury and mercury, of course, rises in small tube l5. A means for reducing the pressure, such as a vacuum pump, is attached to outlet 23 and as the pressure on the system is reduced, the level of the mercury in small tube 15 falls to the level indicated by dashed line 26'. The fritted glass plate I! is thus uncovered and air flows through small tube l5, the uncovered area of fritted glass plate I! and thence through lines I6, 2|, and 22 to outlet 23; this causes the vacuum to be momentarily lowered and the mercury level in arm 14 then rises until the mercury covers the fritted glass plate I I, thus stopping the flow of air.

The impervious plate 11 is located at a point on the inclined arm l4 so that the slightest change in the level of mercury in reservoir II will be multiplied at point I7 and give high sensitivity. The feature of the pervious plate in combination with the inclined arm [4 allows gradual exposure of the pervious plate as the mercury level drops and thus assures high sensitivity.

The auxiliary valve 25 is placed in side arm 22 for use whenever the capacity of the exhaustion means exceeds that of the pervious plate l7. However, it must be emphasized that the valve 25 in no way reduces the sensitivity of the device. Since the system is employed with a fixed amount of fluid heavy metal, the apparatus is designed for raising or lowering the inclined arm [4 and, therefore, the pervious plate I1, when the subatmospheric pressure is to be regulated over a range of conditions. For example, if it were desired to change the pressure regulation from 750 mm. differential, the pervious plate I"? would be raised 10 mm. in elevation for a control of 740 mm. differential.

While the apparatus of the present invention has been described with reference to adjusting the pressure differential for control by raising or lowering the inclined arm l4, it will be apparent that the same end may be achieved by decreasing or increasing the amount of mercury in the system. If it is desired to fix rigidly the arms I and I6, and the inclined arm 14 in which plate I! is located, means such as a suitable valving arrangement, not shown, may be provided at a convenient point in the system such as in pipe 12 for introduction or withdrawal of the mercury.

The pervious plate in the present invention is pervious to air ,or other gases but impervious to heavy fluid metals such as mercury and may be a common fritted glass plate. Other media, of

course, which will exclude mercury, for example, and admit air may be substituted therefor.

The nature and objects of the present invention having been fully described and illustrated, what I wish to claim as new and useful and to secure by Letters Patent is:

1. A device for controlling the pressure in a vessel fluidly connected with an exhausting means by a conduit comprising, in combination, a mercury manometer having a first arm open to the atmosphere and a second arm fluidly connected with said conduit, communication means connecting said conduit and the base of said first arm and means pervious to gas but impervious to mercury between said communication means and the base of said first arm.

2. Apparatus in accordance with claim 1 in which the means pervious to gas but impervious to mercury is a fritted glass plate.

3. A device for controlling the pressure in a vessel fluidly connected with an exhausting means by a first conduit comprising, in combination, a first arm open to the atmosphere, a second arm, including a reservoir for mercury,

fluidly connected above said reservoir with said first conduit and fluidly connected below said reservoir with said first arm, a second conduit fluidly communicating with said first conduit and the base of said first arm and a gas pervious but mercury impervious means disposed between said second conduit and said first arm.

4. Apparatus in accordance with claim 3 in which the gas pervious but mercury impervious means is a fritted glass plate.

OLIVER H. P. DAWSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 855,801 Moore June 4, 1907 883,700 Drager Apr. 7, 1908 1,035,894 Moore Aug. 20, 1912 1,987,666 Carlson Jan. 15, 1935 2,232,267 Price Feb. 18, 1941 

